Thursday, January 3, 2013

Reinterpreting hominin climbing abilities

It can be dangerous to infer too
much about function from the physical traces left by extinct animals. Case in
point: the amount of time early hominins spent in trees. Australopithecusafarensis
(creatures that lived over three million years ago typified by the specimen
known as ‘Lucy’) had the foot and ankle structure required to walk upright.
They also lacked the grasping feet possessed by our earlier ancestors and by
modern chimpanzees. Can we therefore assume that Lucy and her ilk were poor
tree climbers? Not so fast, say Vivek Venkataraman, Thomas Kraft, and Nathaniel
Dominy from Dartmouth College. Just look at modern humans who routinely climb
trees today.

The main reason modern
hunter-gatherers climb trees is to acquire honey. In some communities, during
‘honey season’ men will spend a third of their total foraging time collecting
honey. Needless to say, this activity requires much time in trees. Although
some people make use of technology (pegs, harnesses, ropes), there are groups
of people who climb trees without using any external aids.

The authors compared the
agriculturalist Bakiga people with the hunter-gatherer Twa people, all living
near Uganda's Bwindi Impenetrable National Park (a place that sounds like it should be featured in The Princess Bride). Twa men routinely climb trees unassisted, whereas Bakiga men rarely climb trees
at all.

When chimpanzees climb a tree,
they often use the method of grasping the trunk with their hands, planting
their feet flat on the bark and ‘walking’ upward. Such ‘vertical climbing’
requires a high degree of ankle flexation that didn’t seem to be permitted by
modern human anatomy. It turns out that Twa men are able to flex their ankles
to nearly the same degree as chimpanzees and have been documented walking up
trees in the same manner. In addition, Twa men had much longer leg muscle
fibers than Bakiga men. The combination of longer muscle fibers plus flexible
ankles make the Twa extremely accomplished tree climbers despite having modern
human anatomy.

Clearly, if modern humans can be expert climbers, so could
early hominins like Lucy. This certainly doesn’t prove that A.afarensis spent their days in trees, but it does mean that they
could have.

Stochastic Scientist? What's up with that?

Why the Stochastic Scientist? As I'm sure you all know, 'stochastic' is another word for 'random', which is what I intend for the focus of this blog. Although my formal training is as a molecular biologist, there are many other fields of science that are also fascinating and beautiful. It's my intention to blog about which ever scientific discovery or invention catches my, and hopefully your, fancy.

I also hope to inspire people to learn more about science. By choosing among a huge variety of scientific endeavors, I'll undoubtably hit upon something that will pique my readers' interest.

I guess I could have called my blog 'The Joy of Science', but that wouldn't have been quite so random.